U.S. patent number 7,189,005 [Application Number 11/079,416] was granted by the patent office on 2007-03-13 for bearing system for a turbocharger.
This patent grant is currently assigned to BorgWarner Inc.. Invention is credited to Daniel N. Ward.
United States Patent |
7,189,005 |
Ward |
March 13, 2007 |
Bearing system for a turbocharger
Abstract
A bearing system for a turbocharger, simple in design and easy
to manufacture, having desired rotational dynamics of a three piece
bearing design, yet having the superior vibration damping
characteristics of a one piece bearing design. The inboard end of
each journal bearing includes an axial recess for receiving an
outboard end of a cylindrical bearing spacer, thereby axially
locating the journal bearings as well as axially and radially
locating the bearing spacer.
Inventors: |
Ward; Daniel N. (Asheville,
NC) |
Assignee: |
BorgWarner Inc. (Auburn Hills,
MI)
|
Family
ID: |
36971001 |
Appl.
No.: |
11/079,416 |
Filed: |
March 14, 2005 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
|
US 20060204154 A1 |
Sep 14, 2006 |
|
Current U.S.
Class: |
384/286;
384/901 |
Current CPC
Class: |
F01D
25/166 (20130101); F16C 17/18 (20130101); F05D
2220/40 (20130101); F05D 2260/96 (20130101); Y10S
384/901 (20130101); F16C 2360/24 (20130101); F16C
17/02 (20130101); F16C 17/26 (20130101) |
Current International
Class: |
F16C
17/18 (20060101) |
Field of
Search: |
;384/99,286,287,322,398,901 ;417/407 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hannon; Thomas R.
Attorney, Agent or Firm: Pendorf; Stephen A. Akerman
Senterfitt Dziegielewski; Greg
Claims
I claim:
1. A turbocharger bearing assembly comprising: a bearing housing
(16) having a bore (38) extending therethrough; a shaft (26)
extending through said bore (38); a pair of floating journal
bearings (44,46) rotatably mounted within said bore (38) and
rotationally supporting said shaft; and a generally cylindrical
bearing spacer axially interposed between said journal bearings;
wherein said journal bearings axially overlap with, and thereby
radially locate, said bearing spacer.
2. The bearing assembly as in claim 1, wherein the outer diameter
of said bearing spacer is smaller than the outer diameter of said
journal bearings.
3. The bearing assembly as in claim 1, wherein the inner diameter
of said bearing spacer is greater than the inner diameter of said
journal bearings.
4. The bearing assembly as in claim 1, wherein said inboard ends of
said journal bearings respectively exhibit a circumferential step,
and wherein said bearing spacer is radially supported against the
radially inside surface of said circumferential step.
5. The bearing assembly as in claim 1, wherein said inboard ends of
said journal bearings respectively exhibit a circumferential step,
and wherein said bearing spacer is radially supported against the
radially outside surface of said circumferential step.
6. The bearing assembly as in claim 1, wherein said inboard ends of
said journal bearings respectively exhibit first and second
circumferential steps, and wherein said bearing spacer is radially
supported against the radially inside surface of one of said
circumferential steps and is radially supported against the
radially outside surface of the other of said circumferential
steps.
7. The turbocharger bearing system of claim 6, wherein said journal
bearings have an axially centered lubricating radial oil flow
bores.
8. The bearing assembly as in claim 6, wherein said bearing spacer
includes openings through which lubrication oil can flow.
9. The bearing assembly as in claim 1, wherein said housing (16)
further includes an inlet port (54) for a lubricant, said inlet
port (54) being in communication with lubricating oil channels,
said oil channels directed to the top of the journal bearings (44,
46).
10. A bearing assembly comprising: a bearing housing (16) having a
bore (38) extending therethrough; a shaft (26) extending through
said bore (38) and adapted to rotate at high speed with respect to
said housing (16) and being subjected to axial thrust forces
applied thereto in both axial directions; a pair of floating
journal bearings (44,46) rotatably mounted within said bore (38)
and rotationally supporting said shaft, each journal bearing having
an inner surface in proximity to and encompassing a shaft portion
and an outer surface in proximity to said bore (38), each journal
bearing (44, 46) further having an inboard end and an outboard end;
and a generally cylindrical bearing spacer axially interposed
between said journal bearings, the inner diameter of said spacer
being greater than the outer diameter of said shaft, and the outer
diameter of said spacer being smaller than the inner diameter of
said bore (38); wherein the outer surface area of each journal
bearing is greater than the inner surface area, and wherein said
inboard end of each journal bearing includes an axial recess for
receiving an outboard end of said bearing spacer, the bearing
spacer thereby axially locating said journal bearings, and the
journal bearings radially locating said bearing spacer.
Description
FIELD OF THE INVENTION
The present invention relates to a turbocharger for an internal
combustion engine and more particularly to an improved turbocharger
journal bearing and bearing spacer system.
BACKGROUND OF THE INVENTION
Turbochargers are unique mechanical devices in that they are
expected to operate at extremely high RPM under conditions of high
temperature and changing load, and yet are expected to provide long
trouble-free service.
More specifically, a turbocharger is a type of forced induction
system. Engine exhaust gases drive a turbine. The turbine is
connected via a shaft to a compressor. Ambient air is compressed by
the compressor and is fed into the intake manifold of the engine,
allowing the engine to combust more fuel, and thus to produce more
power for a given displacement. Considering the volumetric gas
intake requirements of an engine operating at peak performance and
the comparatively small size of a turbocharger, it can be
appreciated that a turbocharger may be expected to rotate at speeds
of up to 300,000 rpm.
The basic purpose of a bearing system is to provide a near
frictionless environment to support and guide this rapidly rotating
shaft over the life of the turbocharger, which should ideally
correspond to that of the engine, which could be 500,000 1,000,000
km. The bearing system usually comprises two spaced-apart bearings,
which function to dampen oscillations. Considering that the turbine
is driven by engine exhaust gas, which may have a temperature as
high as 1,300 F, it will be apparent that the bearing system must
be designed so that a sufficient amount of lubricant is always
channeled through the bearing system for removal of heat.
Obviously, the turbocharger bearing system is a critical system
that must be highly engineered.
On the other hand, it is highly desirable to design a turbocharger
that is comprised of a minimum number of parts, which parts are
easy to manufacture and easy to assemble, while still satisfying
the demand for extended service life. Significant design effort has
been directed toward improvements in turbocharger bearing
systems.
In one popular turbocharger design the shaft is supported by a pair
of floating radial bearings arranged in a cylindrical bore formed
in the center housing (also referred to as the bearing housing) of
the turbocharger. In this conventional bearing arrangement, the
axial movement of each of the floating radial bearing is restricted
by a pair of snap rings which are fitted into ring grooves formed
on the inner wall of a cylindrical bore through the turbocharger
center housing. See, for example, the turbocharger journal bearings
described in U.S. Pat. Nos. 3,058,787 and 4,427,309. However, in
the case wherein the floating radial bearings are axially
restricted by a pair of snap rings, a problem occurs in that the
end faces of the rapidly rotating floating radial bearings contact
the stationary snap rings. This contact not only causes friction
wear at the contact area, it may change the rotational speed of the
bearing. In addition, a complicated machining process is necessary
to form the four ring grooves on the inner wall of the cylindrical
bore into which the snap rings must be seated, and, as a result,
the manufacturing cost of the turbocharger is increased. Further,
the seating of four snap rings is labor intensive. As the expected
life of the engine increases, the turbocharger must be engineered
for longer life.
An improvement came with the evolution of the "one piece" radial
bearing assembly, in which the pair of floating radial bearings is
connected by a cylindrical spacer. This eliminated the need for the
respective inboard snap rings, and consequently reducing machining
and assembly costs. Being one solid piece, this design was thought
to provide good vibration damping characteristics. However, in such
a radial bearing assembly, since the axial length of the radial
bearing assembly is very long, and since the two bearings are
rigidly connected and can not independently optimally adjust their
position in the bore, there was a problem in that a complicated and
precise machining process was necessary. In addition, since the
bearing assembly is one continuous piece, any vibration due to
shaft dynamics at one bearing end is instantly communicated to the
other bearing end, and further, heat from the turbine side bearing
is conducted through the thermally conductive metal spacer cylinder
to the compressor side bearing. In addition, lubricating oil
located in the sliding zone of the floating radial bearings cannot
easily escape, and the friction loss of the floating radial
bearings is increased.
In view of the above, U.S. Pat. No. 4,358,253 proposed to install a
separate cylindrical "bearing spacer" axially between the pair of
journal bearings. This bearing spacer was in the form of a tube in
the space between a stationary housing and the rapidly rotating
shaft. However, given the rapid flow of oil in this space, in order
to stabilize and prevent "wobble" of the bearing spacer, the spacer
was given an outer diameter corresponding substantially to that of
the outer diameter of the bore. This greatly diminished or even
completely stopped the rotation of the spacer, and thus prevented
wobble. However, this spacer design tends to impede oil flow.
Further, since the bearing spacer exhibits little or no rotational
speed, wear is produced where the spacer contacts the rapidly
rotating journal bearings. Further yet, given the high rotational
speed of the shaft, the stationary spacer introduces drag and
contributing to accelerated oil degradation in the space between
the shaft and spacer.
It has also been proposed to utilize a bearing spacer having an
inner diameter corresponding substantially to the outer diameter of
the roatary shaft. While this snug fit would prevent wobble, such a
close fit between bearing spacer and shaft causes the bearing
spacer to rotate a high speed, causing shear and oil degradation,
as well as drag on the shaft.
These prior designs utilizing a separate central bearing spacer
have all proven satisfactory with regard to providing proper axial
spacing of the radial bearings. However, the need to prevent wobble
of the bearing spacer required the bearing spacer, if not integral
with the bearings, to be either snugly fit to the shaft or snugly
fit the bearing housing bore. These designs, though overcoming the
problems associated with the four snap-ring design, have not
provided adequate oil flow over and about the inner and outer
diameter surfaces of the journal bearings and have not achieved
satisfactory rotational speeds of the bearing spacer for reduction
in drag, and as a result have suffered from relatively premature
journal bearing failure.
As an improvement over the above described bearing spacers is
provided in U.S. Pat. No. 4,902,144 entitled "Turbocharger Bearing
Assembly", teaching a bearing design employing a pair of journal
bearings separated by a floating central spacer. The generally
cylindrical, rotationally floating bearing spacer has opposite ends
defining a pair of axially outwardly presented inboard thrust
surfaces to maintain the two journal bearings in precision axial
spaced relation. For radially locating or "piloting" the bearing
spacer within the center housing bearing bore, the spacer exhibits
pilot means radiating outwardly from the spacer outer diameter.
This design allows unimpeded oil flow and thus achieves an improved
oil flow over the journal bearings in comparison to the bearing
system described in U.S. Pat. No. 4,358,253. However, the design of
the bearing spacer is complex and thus is associated with
manufacturing expense. Further, considering the changes in
temperature, viscosity, and rotational speed of the turbocharger,
it is difficult to design the spacer to have optimal rotational
speeds over the entire rotational speed range of the turbocharger
rotary shaft. Further yet, the three-piece design with the
freely-floating bearing spacer lacks the inertia related
stabilizing effect of the one-piece bearing spacer on any radial or
rotational vibration of the journal bearings. Thus, one of the
advantages of the "one piece" bearing system is missing in this
"three piece" bearing system design.
Accordingly, there is a need for a simpler, easier to manufacture,
lower cost bearing system for a turbocharger that achieves desired
rotational dynamics of the three piece design, yet achieves the
superior vibration damping characteristics of the one piece design,
and yet does not suffer from the requirement for precise machining
of the one-piece bearing.
SUMMARY OF THE INVENTION
The present invention overcomes the problems and disadvantages
encountered in the prior art by providing an improved turbocharger
bearing system wherein the bearing spacer is not only axially
located by the bearings, but is additionally radial located by the
bearings.
For this, the bearing inboard faces are provided with either a
cylindrical axial protrusion or recess, and the bearing spacer is
provided with a mating recess or protrusion, such that the bearing
spacer is both axially and radially constrained.
Since the bearing spacer has a greater amount of surface area in
contact with the bearings, it will rotate at approximately the same
speed as the bearings, which is optimal. Since the bearing spacer
does not have radial "pilot" protrusions, it will not cause shear
of oil, will not introduce drag to impede rotation of the
turbocharger. Since the bearing system is not a one-piece system,
it will fit to the turbocharger without requiring precise
machining. Since the bearing spacer is radially supported by the
bearings, vibration can be transmitted from one bearing to the
other to a limited extent, thus providing some inertial damping of
vibration not possible with a free-floating bearing spacer. Since
the three bearing pieces rotate at the same speed, friction wear is
reduced. Since the bearing spacer is radially supported, the
bearing spacer exhibits resistance to wobble. The invention also
provides a bearing system that is simple and relatively inexpensive
to manufacture, easy to assemble, and is highly durable.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is illustrated by way of example and not
limitation in the accompanying drawings in which like reference
numbers indicate similar parts, and in which:
FIG. 1 is a side cross-sectional view of a turbocharger
incorporating a bearing system constructed in accordance with the
present invention.
FIG. 2a is an enlarged, cross-sectional view of a preferred
embodiment of the bearing system of the present invention.
FIGS. 2b d show details of three possible designs of bearings
securing the bearing spacer axially as well as radially.
DETAILED DESCRIPTION OF THE INVENTION
The illustrative turbocharger 10 depicted in FIG. 1 includes
turbine wheel in a turbine housing, a compressor wheel in a
compressor housing, a shaft connecting the two wheels, and a
bearing system for rotationally and axially supporting the
shaft.
The turbine more specifically comprises a turbine wheel 22 and a
turbine housing 30 such that exhaust gas is guided to the turbine
wheel 22 by the housing. The inertia and expansion energy in the
exhaust gas turns the turbine. Once the gas has passed through the
blades of the turbine wheel it leaves the turbine housing 30 via
the exhaust outlet area 42. If the engine is in idle mode the wheel
will be spinning at a lower speed, and as more gas passes through
the turbine housing the turbine wheel will rotate faster.
The function of the compressor is opposite to that of turbines. The
compressor uses the energy, which has been extracted from the
exhaust gas in the turbine by slowing and expanding (thereby
cooling), in order to accelerate and compress (thereby heating)
ambient air for the engine intake. The compressor is comprised of
two sections--the compressor wheel 26 and the compressor housing
34. The compressor wheel 26 is connected to the turbine by a shaft
20. As the compressor wheel 26 spins, air is drawn in via an air
inlet 44 and is compressed as the blades spin at a high velocity.
The compressor housing 34 includes a volute portion designed to
convert the high velocity, low pressure air stream into a high
pressure, low velocity air stream through a diffusion process,
thereby providing increased mass flow through the engine for
increased performance and power output.
The turbocharger of the present invention includes an improved
bearing arrangement for rotatably supporting the shaft 20. The
journal bearings 16 and 18 are of the free-floating rotational
type. The journal bearing has inner and outer bearing surfaces.
Usually the speed differential between the shaft and the journal
bearing inner bearing surface is very high, and the speed
differential between a journal bearing outer bearing surface and
bearing housing is comparatively low. Thus, the oil film on the
outer diameter of the journal bearing acts as a damper, and does
not experience a high shear rate. The inner diameter of the journal
bearing is smaller than the outer diameter. Thus, although higher
shear forces act on the inner diameter of the journal bearing, the
smaller total surface area of the journal inner bearing surface
ensures that the journal bearing does not rotate too rapidly. The
surface areas can be adjusted by beveling or otherwise reducing
surface area.
The turbocharger bearing system is lubricated by oil from the
engine. The oil is fed under pressure into the bearing housing 36
to lubricate the bearing surfaces within and about the journal
bearings. Oil passes through individual bearing supply ports 31 and
32 for lubricating the journal bearings 16 and 18. These supply
ports 31 and 32 open at generally axially centered positions with
respect to the two journal bearings, such that oil flow may occur
in both directions axially to lubricate the bearing surfaces.
Journal bearings 16 and 18 have axially centered lubricating oil
flow bores 12. Oil flowing over and through the journal bearings 16
and 18 is eventually collected within a bearing housing sump
chamber 40 for return circulation through an outlet port 46.
As shown in more detail in FIG. 2a, the journal bearings 16 and 18
have a generally conventional sleeve bearing construction which can
be formed by various manufacturing techniques utilizing a variety
of known bearing materials, such as leaded or unleaded bronze,
aluminum, etc. The journal bearings 16 and 18 have inner diameter
surfaces sized to fit with relatively close clearance about the
shaft 20.
As in the the prior art, the improved turbocharger bearing assembly
includes bearing spacer 14 for precise axial location and retention
of the journal bearings 16 and 18. In contrast to the prior art,
the journal bearings 16 and 18 provide secure radial location and
retention of the bearing spacer 14 for effectively substantial
clearance relative to the shaft 20 and the bearing bore 38,
respectively, to permit substantially unimpeded oil flow from the
journal bearings in the inboard direction and to provide acceptable
rotational speed of the journal bearings 16 and 18 and bearing
spacer 14 at different shaft rotational speeds. The journal
bearings are not rigidly connected to the bearing spacer, thus they
can conform to the alignment and geometry of the bearing bores, and
there is no critical requirement for precise machining as in the
case of the prior art one-piece bearing spacer.
More specifically, the journal bearings 16 and 18 are each
constructed such that, in the inward facing axial thrust surface, a
shape such as a step or recess or cylinder is formed 16a (18a). The
bearing spacer outer thrust surfaces are adapted to fit freely
slidingly in these recesses. The invention is characterized by an
area of axial overlap between bearing and bearing spacer, such that
the bearing spacer is radially located.
The provision of the recess in the bearings 16 and 18 provides a
relatively simple design adapted to locate and retain the bearing
spacer 14 in precision spaced relation.
In addition, the journal bearings 16 and 18 include outer diameter
surfaces sized to fit with relatively close clearance within an
axially elongated bearing bore 38 formed within the bearing housing
36. In the preferred form, the bearing bore 38 has a uniform
diametric size to permit simple slide-in reception of the journal
bearings, which are sized in turn for rotational floating within
the bearing bore 38 during rotation of the shaft 20.
The bearing spacer 14 provides a component adapted to locate and
retain the bearings 16 and 18 in precision spaced relation. The
spacer 14 can be constructed from a low cost plastic selected to
withstand typical turbocharger operating temperature ranges. If
constructed of metal, the thickness of the bearing spacer need not
be substantial. The bearing spacer may even be formed from a sheet
of metal rolled into a tube, such that insertion of this sub into
cylindrical recesses in the bearings prevents opening of the
tube.
As shown in FIG. 2a, the outer diameter of the spacer 14 is formed
on a diameter substantially less than the outer diameters of the
journal bearings 16 and 18. Similarly, the inner diameter of the
bearing spacer 14 is formed on a diameter significantly greater
than the inner diameter of the journal bearings 16 and 18.
Furthermore, the spacer 14 has large lubricating oil flow central
output opening.
The improved turbocharger bearing assembly of the present invention
thus provides relatively simple bearing components which can be
installed by simple slide mounting onto the turbocharger shaft and
within the bearing bore, as part of the overall turbocharger
assembly process.
Although the bearing system has been shown in FIG. 2a with the
radially-locating step in the bearing being radially outward of the
bearing spacer as shown in greater detail in FIG. 2b, the invention
is not limited to this embodiment, but includes embodiments wherein
the step formed in the bearing is located radially inside of the
bearing spacer as shown in FIG. 2c, or the bearing may have two
steps, one radially ouside and one radially inside the bearing as
shown in FIG. 2d.
While the invention has been described by reference to a specific
embodiment chosen for purposes of illustration, it should be
apparent that numerous modifications could be made thereto by those
skilled in the art without departing from the spirit and scope of
the invention.
The contact surface between bearing spacer and bearing need not be
perfectly cylindrical. The ends of the spacer could be castellated,
or the bearing inward facing sufaces could be a series of
protrusions. However, for manufacturing purposes, the cylindrical
design shown in the figures is easiest to produce.
Importantly, the improved bearing system comprises relatively
simple components adapted for rapid yet accurate assembly to reduce
the overall manufacturing complexity and cost of the turbocharger.
Moreover, the bearing components are designed for enhanced bearing
oil flow to achieve prolonged bearing life with minimal heating and
wear. It is to be understood, however, that the bearing structure
of the present invention is useful in conjunction with a variety of
turbocharger assemblies, and is not to be limited to use with the
particular turbocharger described herein.
Now that the invention has been described,
* * * * *